1. Field of the Invention
The invention is related to the field of communications, and in particular, to control systems for call processors that process emergency calls from mobile communication devices.
2. Description of the Prior Art
FIG. 1 illustrates emergency call system 100 in an example of the prior art. Emergency call system 100 includes mobile communication device 101, communication network 102, location system 103, Global Positioning Satellite (GPS) system 104, and Public Safety Answering Points (PSAPs) 111-113.
Mobile communication device 101 communicates over the air with a sector of a cell site in communication network 102. Communication network 102 is coupled to location system 103 and PSAPs 111-113. Location system 103 is coupled to GPS system 104 and PSAPs 111-113. GPS system 104 and mobile communication device 101 exchange communications.
FIG. 2 illustrates an emergency call in an example of the prior art. Mobile communication device 101 places an emergency call to communication network 102—typically by calling 911. In response to receiving the emergency call from a mobile device, communication network 102 transfers a call request to location system 103. The call request indicates the cell site and the cell sector in communication network 102 that received the emergency call from mobile device 101.
In response to the request, location system 103 enters a database with the cell site and sector to yield an Emergency Service Routing Key (ESRK). The key is associated with the PSAP that will handle the emergency call to dispatch emergency responders. Location system 103 transfers the key to communication network 102. Communication network 102 routes the emergency call to the appropriate PSAP based on the key. Communication network 102 also transfers the key to the appropriate PSAP over the emergency call. In this example, communication network 102 routes the emergency call to PSAP 111 based on the key, and transfers the key to PSAP 111 over the emergency call.
In response to the emergency call, PSAP 111 transfers the key to location system 103. In response to the key from PSAP 111, location system 103 enters the database with the key to yield a location for mobile device 101. Location system 103 transfers the location for mobile device 101 to PSAP 111. In this example, the location is a “Phase I” location that is indicated by the street address of the cell site, the direction of the cell sector, and the size of the cell sector. PSAP 111 transfers this location to the responding emergency personnel.
FIG. 3 illustrates an emergency call in another example of the prior art. In this example, mobile communication device 101 has a GPS receiver to detect GPS signals. Mobile communication network 101 places an emergency call to communication network 102. In response to receiving the emergency call from mobile device 101, communication network 102 transfers a call request to location system 103. The call request indicates the cell site and cell sector in communication network 102 that received the emergency call. The call request also indicates that mobile device 101 has GPS capability.
Location system 103 enters a database with the cell site and cell sector to yield the key. Location system 103 transfers the key to communication network 102. Communication network 102 routes the emergency call to the appropriate PSAP based on the key, and transfers the key to the appropriate PSAP over the emergency call. In this example, communication network 102 transfers the emergency call and key to PSAP 111.
In response to the emergency call, PSAP 111 transfers the key to location system 103. In response to the key from PSAP 111, location system 103 enters the database with the key to yield the Phase I location (street address of the cell site, direction of the cell sector, and the size of the cell sector). Location system 103 transfers the Phase I location to PSAP 111.
In response to the emergency call from a mobile device with GPS capability, location system 103 transfers a GPS query that identifies mobile communication device 101 to GPS system 104. In response to the query, GPS system 104 transfers a GPS request to mobile communication device 101. In response to the request, mobile communication device 101 transfers a GPS response with GPS signal information to GPS system 104. GPS system 104 processes the GPS signal information to determine the GPS coordinates for mobile communication device 101. GPS system 104 transfers the GPS coordinates to location system 103. Location system 103 stores the GPS coordinates in association with the key.
In response to the emergency call from a device with GPS capability, PSAP 111 re-transfers the key to location system 103. In response to the re-transferred key, location system 103 enters the database with the key to yield the GPS coordinates for mobile device 101. Location system 103 transfers this location for device 101 to PSAP 111. In this example, the location is a “Phase II” location that is indicated by the GPS coordinates. PSAP 111 transfers the Phase I and II locations to the responding emergency personnel.
There are some constraints placed on location system 103. Location system 103 will not attempt to query GPS system 104 for GPS coordinates if the cell sector receiving the emergency call is classified as small. This classification is based on a sector sizing parameter. If the cell sector is smaller than the sector sizing parameter, then the cell sector is designated as small, and GPS coordinates are not determined for emergency calls from that cell sector.
When location system 103 obtains GPS coordinates for mobile device 101, location system 103 increases a GPS uncertainty factor for the GPS coordinates over time because device 101 could be moving. The increase is based on a GPS uncertainty parameter that is specified in meters per second. For example, if the GPS uncertainty parameter is 30 meters per second, and the GPS coordinates are four second old when provided to the PSAP, then location system 103 adds a GPS uncertainty factor of 120 meters (30 m/sec×4 sec) to the GPS coordinates. If the GPS uncertainty factor becomes too large, then location system 103 does not even transfer the GPS coordinates to the PSAP.
If location system 103 does not receive GPS coordinates from GPS system 104 within a specified time after its initial GPS query, then location system 103 will re-query GPS system 104. For example, if the GPS re-query parameter is 100 seconds, then location system 103 waits 100 seconds after its initial GPS query without any response before re-querying GPS system 104 for the GPS coordinates.
Location system 103 returns the key to communication network 102 after a key timing parameter. For example, if the key timing parameter is 100 milliseconds, then location system 103 waits 100 milliseconds before transferring the key to communication network 102. Unfortunately, communication network 102 may establish the voice path for the emergency call between mobile device 101 and PSAP 111 before mobile device 101 has finished interacting with GPS system 104. When mobile device 101 attempts to interact with GPS system 104 and handle the voice path at the same time, mobile device 101 may drop the voice path for the emergency call to PSAP 111.
Thus, there are various parameters that location system 103 uses to handle emergency calls. Note that one set of parameters may work well for one PSAP, but these parameters may not work so well for another PSAP. If the parameters do not work well for the other PSAP, then GPS locations may not be provided to the other PSAP on some emergency calls. When a precise GPS location is not provided, emergency responders must rely on the less precise Phase I location (cell site address, sector direction, and sector size). The lack of a precise GPS location could delay the emergency responders, and thus, could be the difference between life and death for the emergency caller.
For example, the above described parameters for PSAPs 111-113 could be:                Sector sizing parameter: 1000 meters;        GPS uncertainty parameter: 30 meter per second;        GPS re-query parameter: 100 seconds; and        Key delay parameter: 100 milliseconds.        
These parameters may work well for PSAPs 111-112, but they may work poorly for PSAP 113. As a result, PSAP 113 may not get precise GPS locations for mobile devices with GPS capability. To address the problem, new parameters could be used for PSAPs 111-113 as follows:                Sector sizing parameter: 250 meters;        GPS uncertainty parameter: 10 meter per second;        GPS re-query parameter: 25 seconds; and        Key delay parameter: 2000 milliseconds.        
The new parameters may work well for PSAPs 112-113, but they may work poorly for PSAP 111. Unfortunately, the current implementation of these parameters may block the use of GPS locations on emergency calls that should provide GPS locations. The failure to provide GPS locations on these emergency calls could have grave consequences for the caller.